Conventional residential, light industrial and commercial circuit breakers typically have a thermal trip mechanism which responds to persistent overcurrents of moderate magnitude to provide a delayed trip in the breaker. Also included in the circuit breaker is a magnetic trip mechanism which responds instantaneously to overcurrent conditions of greater magnitudes. It is becoming more common for these circuit breakers to further include a ground fault trip mechanism as one of the active mechanisms. The ground fault trip mechanism includes a trip unit which detects faults between the line conductor and ground and the neutral conductor and ground. Line to ground faults are commonly detected by the use of a differential transformer. The line and neutral conductors are passed through the coil so that in the absence of a line to ground fault, the currents are equal and opposite and no signal Is generated. However, when a line to ground fault exists, it creates a sizeable imbalance between the two currents in the two conductors which can be level detected. As is known, a neutral to ground fault may be detected by injecting a signal onto the neutral conductor which will produce an oscillation if feedback is provided.
In addition, conventional circuit breakers include mechanisms designed to protect against arc faults. For example, an arc fault may occur in the device when bare or stripped conductors come into contact with one another and the current caused by such a fault produces magnetic repulsion forces which push the conductors apart, thereby striking an arc. The arc that is caused by these faults can damage the conductors by melting the copper therein and this is especially true for stranded wire conductors such as extension cords, which can ignite surrounding materials.
Typically, the circuit breaker includes contacts that open upon sensing arcing from line to ground and/or from line to neutral. Arc fault circuit breakers typically use a differential transformer to measure arcing from line to ground. Detecting arcing from line to neutral is accomplished by detecting rapid changes in load current by measuring voltage drop across a relatively constant resistance, usually a bi-metal resistor.
Unfortunately, many conventional circuit breakers, including residential circuit breakers, do not permit the user to test both the arc fault circuit interrupter (AFCI) and ground fault circuit interrupter (GFCI) circuits in the device. On the other hand, if these circuit breakers allow the user to test both the AFCI and GFCI circuits, these circuit breakers necessitate the use of an opto-coupler to pass the trip signal while electrically isolating the two line phases from the detection circuitry. In addition, the prior art requires using two test switches, one switch for each phase, testing both ground fault and arc fault. Furthermore, the ability to test both of these detection circuits is very important for customer safety and because a vast amount of individuals do not understand the implications of a circuit failure, it is important to best educate these individuals about these implications and what systems are available to minimize the likelihood that such a circuit failure occurs.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a method and apparatus for a circuit breaker having an arc fault detection circuit, a ground fault detection circuit, a signal indicative of an arc fault in a corresponding pole of the circuit breaker; and a trip mechanism including a pair of separable contacts. The trip mechanism is in operable communication with the ground fault detection circuitry so that in response to receiving the signal from the ground fault detection circuitry, the arc fault detection circuitry causes the ground fault detection circuitry to generate a trip signal causing the trip mechanism to separate the pair of separable contacts. In an exemplary embodiment, a switch assembly is included for switching to a corresponding pole to test arc fault and ground fault functionality. The switch assembly is switchable between a first position and a second position corresponding to two different poles of the circuit breaker. The first position comprises a test position for an AFCI circuit associated with one pole and the second position comprises a test position for another AFCI circuit associated with another pole. In either the first or second position, AFCI circuitry initiates a trip by generating a current imbalance causing the GFCI circuitry to generate a trip signal for tripping the circuit breaker. Thus, the present disclosure permits the customer to test both the AFCI and GFCI circuits by positioning a switch assembly accordingly in either the first or second test button positions.